A comparison of lung mast cells with gastrointestinal mast cells from the same monkey reveals both similarities and differences. Both populations of cells degranulate to anti-human IgE, but not to compound 48/80. Degranulation induced by anti-IgE in both mast cell populations is inhibited by theophylline and quercetin. However, in comparison to gastrointestinal mast cells, lung mast cells stain more readily, have a higher histamine content, and release more mediators upon stimulation, confirming mast cell heterogeneity and the need to characterize mast cell populations in higher animals. Cultured mouse mucosal mast cells degranulate upon exposure to N-acetyl cysteine, a mucolytic agent. Mucosal mast cell degranulation is inhibited by sulphasalazine. Aspartame has little or no direct effects on mast cells and basophils. Patients with a history of immediate adverse reactions to foods and whose symptoms are reproduced on challenge, are atopic, have multiple positive skin tests to foods and inhalants, have a positive skin test to the food in question, and by history are those with the most severe reactions. Twenty-five patients with idiopathic anaphylaxis, and eight with systemic mastocytosis have been challenged with sulfites. No clinical reactions were observed, although plasma histamines were elevated following challenge. One severe reactions to sulfites was observed in an asthmatic.